The use of displays in a Magnetic Resonance Imaging (MRI) equipment environment was first developed in the late 80's and early 90's, as described in U.S. Pat. Nos. 5,412,419, 5,432,544, 5,627,902, and 5,877,732.
MRI is one of the fastest changing imaging modalities in the world. In addition to the use of MRI for the diagnostic purpose, other applications such as functional MRI (fMRI) have been a major use of this imaging modality. The fMRI field requires various stimulation tasks such as an auditory and visual delivery system along with eye tracking to record the movements of the eyes during the procedure.
The current technology for displaying visual stimuli and recording the eye movement in functional MRI applications has many limitations due to the constraint of the strong magnetic field and high-energy radio frequency signals.
In both the goggle display type and the visor display type, the current technology uses very fine mesh in front of the actual display to block the emission of the RF to the outside and cause interference to the MRI signal. The mesh will create some disturbance to the visual effect of the display for the subject undergoing the functional MRI.
Eye-trackers in most cases are video-based, meaning there is a camera located outside of the bore of the MRI magnet, or in some designs a coherent fiber optic bundle used, similar to the devices used for endoscopy, to look at the eye. This technology also poses a problem for the researchers, because the set up time is very long and the center of the eye with respect to the camera has to be fixed. A slight movement of the subject's head will throw off the calibration of the eye tracker. The eye is looking to a display for presenting stimuli to the subject and the eye tracker camera has to look to the corner of the eye to observe the eye from under the eye LED.
Currently, most facilities use a video projector or LCD display located on the back of the magnet and the subject has to look into a reflective mirror to view the images. This make the tracking of the eye at the same time more difficult. Because the subject has to be able to look at the video projected to him/her either through the reflected mirror or via the optical lens, the path of the camera looking at the center of the eye will be blocked; therefore the MRI operator has to fix the camera to look at the eye with an angle not perpendicular to the eye. This causes the eye tracker to lose track as the eye moves farther away from the center.